This invention relates to a method of operating a touch-screen device and to a touch-screen device. The invention provides a system and method for emulating pressure sensitivity on multi-touch devices.
Graphics tablets are commonly used for creating digital drawings. Graphics tablets, because of their stylus-based interface, have the ability to distinguish applied user pressure. The pressure-sensitivity can be used to control line thickness, opacity, and/or colour, for example. There are similarities between multi-touch devices such as modern smartphones or tablet computers and graphics tablets, and it is tempting to think of using a phone or tablet and fingers, instead of a graphics tablet and a stylus. Several drawing/painting applications already exist for popular touch-screen devices that are based on this principle.
The main drawback expressed by graphic designers when using such touch-based devices today is the lack of pressure detection in devices such as smartphones and tablet computers. Current devices such as mobile phones and tablet computers do not have a pressure sensitive multi-touch surface, and therefore cannot perform pressure detection, unlike graphics tablets. An existing solution is to associate an additional device to the multi-touch device, for example a stylus. Several types of stylus exist today that are compatible with multi-touch devices, but very few of them are sufficiently accurate at passing pressure information back through the stylus to the device. All such additional devices suffer from the same drawbacks: an additional cost, the divergence from the basic user experience that uses fingers for everything, and implementation issues involved in trying to track the size of a touch since the feature is not always possible, permitted, or documented on certain devices.
To control line thickness, another solution has been identified, which consists of drawing lines at a fixed weight and reshaping the lines by erasing some parts. The drawback of this technique is that this is a laborious task for all but the most simplest of drawings. The technique requires the reworking of each line, possibly in different layers to avoid unwanted erasing. This approach only works to control line thickness, and is not suitable for other attributes such as opacity or colour.